1. Field of the Invention
The present invention relates to a rotor and a motor having the same.
2. Description of Related Art
As disclosed in Japanese Unexamined Patent Publication No. 2002-234449, a rotor of a brushless motor, which is used in a power steering system, includes a cylindrical shaft. One such cylindrical shaft is shown in FIG. 10. As shown in FIG. 10, a stator 55 is secured to an inner peripheral surface of a housing 54 of a brushless motor 53 of a power steering system 51. A rotor 57 is rotatably received at radially inward of the stator 55 in such a manner that the rotor 57 is radially spaced a predetermined distance from the stator 55. Magnets 56 are installed to an outer peripheral surface of the rotor 57. Wheels (not shown) are connected to axial ends, respectively, of a rack shaft 59. Rotation of the rotor 57 causes reciprocal movement of the rack shaft 59 through a ball screw mechanism 58. In this way, a steering force of a steering wheel 52 is assisted by the brushless motor 53.
The rack shaft 59 is inserted through the rotor 57. As shown in FIG. 11A, a double sided portion (a positioning portion) 61, which includes two diametrically opposed flat sides, is formed at one end of a cylindrical shaft (a rotor shaft) 60 of the rotor 57. As shown in FIGS. 11A and 11B, a key groove 62 is formed in an outer peripheral surface of the cylindrical shaft 60. The double sided portion 61 is formed to prevent, for example, rotation of the cylindrical shaft 60 at the time of installing a nut into the other end of the cylindrical shaft 60. More specifically, the double sided portion 61 is held by an assembly device to position and secure the cylindrical shaft 60. The key groove 62 is formed to position a sensor or the like, which is installed to the cylindrical shaft 60.
In the case of the above cylindrical shaft 60, after formation of the cylindrical shaft 60, additional manufacturing steps for forming the double sided portion 61 and the key groove 62 are required. This causes an increase in the number of manufacturing steps, thereby resulting in an increase in the manufacturing costs. Furthermore, at the time of installing the sensor or the like to the cylindrical shaft 60, the key groove 62 needs to be detected in the circumferential direction in the surface of the cylindrical shaft 60 to position the sensor or the like relative to the key groove 62, resulting in a low work efficiency.